The present disclosure generally relates to fastener-driving tools for driving fasteners into workpieces, and more particularly relates to pneumatic-powered fastener-driving tools, also referred to as pneumatic tools or pneumatic nailers.
Fastening tools, and particularly those being pneumatically powered, incorporate a housing enclosing a cylinder. Slidably mounted within the cylinder is a piston assembly in communication on one side with a supply chamber and a return chamber on the opposite side thereof. The piston assembly includes a piston head and a rigid driver blade that is disposed within the cylinder. A movable valve plunger is oriented above the piston head. In its at-rest position, this valve plunger prevents the drive chamber from communicating to the piston assembly and allows an air flow path to atmosphere above the piston assembly. In its actuated state, the valve plunger prevents or blocks the air flow path to atmosphere and allows an air flow path to the drive chamber. Exemplary pneumatic nailers, are disclosed in commonly assigned U.S. Pat. No. 4,932,480, and U.S. Patent Application Publication Nos. 2012/0223120 and 2013/0206811; all of which are incorporated by reference.
Combustion powered fastener driving tools also employ a housing having a cylinder with a reciprocating piston and driver blade. Combustion-powered tools are known in the art, and one type of such tools, also known as IMPULSE® brand tools for use in driving fasteners into workpieces, is described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,197,646; 5,263,439; 6,145,724 and 7,341,171, all of which are incorporated by reference herein.
When a tool's actuation requirements have been met, the movable valve plunger opens and exposes one side of the piston assembly to a compressed gas energy source. The resulting pressure differential causes the piston and driver blade to be actuated downwardly to impact a positioned fastener and drive it into a workpiece. Fasteners are fed into the nosepiece from a supply assembly, such as a magazine, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
As the piston is actuated downwardly, it drives the air inside the cylinder through a series of vents into the return chamber increasing the pressure in this chamber. After the fastening event has taken place, the valve plunger moves back to the at-rest position, blocking the supply chamber's air flow path to the piston head and releasing the pressure above the piston head through the path to atmosphere. At this time, the pressure built in the return chamber pushes the piston assembly back up towards the top of the cylinder. The air above the piston head is forced through the valve plunger's air flowpath to atmosphere.
Conventionally, both pneumatic and combustion powered fastening tools include a resilient or elastomeric bumper for arresting axial movement of the piston in a driving stroke. As the piston reciprocates within the cylinder for driving the fasteners into the workpieces, the bumper is repeatedly engaged by the piston, thereby affecting its response to heavy impacts, and air circulation along its outer surfaces. Such a bumper requires high tensile strength, high endurance to breakage, high tear strength, high fatigue strength, and low changes in elasticity over a wide range of operating temperatures, e.g., ranging from about −20° F. to about 200° F.
Heat is generated by internal friction due to the repeated heavy impacts of the piston on the bumper. As is known in the art, multiple slots and bores of various shapes are provided for cooling the bumper during operation. Although some heat build-up and impact-related fatigue can be reduced by the slots and bores, some conventional bumpers exhibit breakage and collapse after prolonged use, all of which prevent an adequate blade return during cycling of the piston. Therefore, there is a need for improving the bumper that provides a better cooling design while upholding the overall bumper rigidity and durability.